Safety systems for nuclear reactors are known which implement digital computing modules as part of the reactor protection system. These modules implement standard digital techniques such as are used in computers. The essence of these techniques is the conversion of input signals to digital form, storage in memory, the use of a stored program to manipulate the stored data and the presentation of an output. All of these functions are essentially performed serially in the time domain by a single central computer.
The disadvantage of such prior art systems is the length of time required to do the calculations in sequence and the complexity of a program that has to manipulate in serial fashion the individual measured parameters. The normal sequence involves the taking in of data parameters to perform a series of calculations and, at the end of the calculations, to produce data which determines whether or not the reactor is in a safe operating posture.
Another problem of such prior art devices comes from the nature of digital computers operating in this fashion causing data to lose identity except for address location. Hence the tracing of programs or the debugging of faults in the system becomes time consuming and difficult. The serial computer system in order to be continuously and exhaustively tested and retested to assure proper safety control require that each of the measured parameters affecting safety have every possible value or state relative to all the other parameters. For example, if possible, reactor temperatures could have 4000 different possible values and pressure having 4000 different possible values and liquid flow 4000 possible values the number of possible input states to the serial machine would be 4000 to the third power. To exhaustively test this, even at the rate of one every tenth second, would require the order of hundreds of years. Thus, other means have been employed to assure that there are no flaws in programs for safety systems. This involves extensive review and checking by independent technical groups and regulatory authorities.